Shark meat sold at retail in the U.S. is often mislabeled or ambiguously labeled, and not infrequently originates from critically endangered species that are dangerously high in mercury, according to a new study led by the University of North Carolina at Chapel Hill.

Published in Frontiers in Marine Science, the study found that, of 29 products tested, 27 were labeled as “shark” or “mako shark,” and of the two samples that had a species-specific label, one was incorrectly labeled. The single sample that was accurately labeled was identified as blacktip shark meat.

The 29 products comprised 11 species of shark, three of which are categorized as Critically Endangered by the International Union for Conservation of Nature (IUCN): great hammerhead, scalloped hammerhead, and tope. The fraudulent meat was being sold sometimes for as little as $2.99 per pound.

Moreover, previous studies have found that hammerhead meat contains very high levels of mercury, which can be damaging to human health, underlining the food safety and human health implications of seafood mislabeling and food fraud.

The researchers purchased 19 shark meat filets from grocery stores, seafood markets, and Asian specialty markets (mostly in North Carolina), and ordered ten shark “jerky” samples online. Using standard DNA barcoding techniques, they identified the samples to the species level.

Per U.S. Food and Drug Administration (FDA) regulations, the acceptable market name for all listed shark species is “shark,” which the researchers say diminishes the regulatory effectiveness of species-specific labeling. The researchers recommend that sellers of shark meat in the U.S. be required to provide species-specific names. They also call for increased monitoring of shark meat and seafood products to improve transparency.